README.md

sql4pandas

Efficient SQL bindings for the pandas data analysis library. Compile and execute sql queries directly on pandas data frames without copying to an external database. Written in pure python (no C extensions), but as it operates directly on pandas dataframes and uses numexpr for further optimizations, is quite efficient compared to other pandas sql modules.

Capabilities

SELECT/SELECT INTO Statements:

• FROM, WHERE, GROUP BY, ORDER BY Clauses
• LEFT, INNER, RIGHT and OUTER JOINS
• CASE Statements
• Basic functions(ie. SUM, MIN, MAX... works with almost any native pandas aggregate function)
• Standard Comparators (ie. <, >, =, !=, <>), 'AND' and 'OR' to chain
• Comparators and arithmetic operations efficiently implemented using numexpr, making them faster and more memory efficient than vanilla python
• aliasing for column names
• nested queries
• arithmetic operations(+, -, /, *...etc)

TODO

• more functions, such as ISNULL statements
• other statement types such as UPDATE, INSERT, DELETE etc
• '?' templating
• performance optimizations
• Syntax checking, validation and explicit error handling for sql errors

DEPENDENCIES

• pandas 13.0+
• numpy 1.8.0+
• numexpr
• sqlparse 0.1.1+
• Tested on Python 2.7.x (untested but should work with Python 3+)

EXAMPLES

>>> import pandas as pd
>>> import numpy as np
>>> from sql4pandas import PandasCursor

>>> tbl1 = pd.DataFrame(np.random.randn(1000, 5) * 50,
                    columns=['a', 'b', 'c', 'd', 'e'])
>>> tbl2 = tbl1.copy()
>>> crs = PandasCursor({'tbl1': tbl1, 'tbl2': tbl2})
>>> crs.execute("""SELECT
        CASE
            WHEN SUM(tbl1.e) > 0
            THEN SUM(tbl1.e)
            ELSE SUM(tbl2.a)
        END AS rand,
        MIN(tbl1.b) as min,
        CASE
            WHEN MIN(tbl1.c) < 0
            THEN MIN(tbl1.c)
            WHEN MAX(tbl2.b) > 0
            THEN MAX(tbl1.e)
            ELSE SUM(tbl1.b)
        END as crazy
       FROM tbl2
           LEFT JOIN tbl1
               ON tbl2.e = tbl1.e
       WHERE tbl1.a > 0 AND tbl2.b < 0
       GROUP BY tbl1.a, tbl2.b
       ORDER BY SUM(tbl1.d)""")
  >>> crs.fetchall()

           rand       crazy         min

  87    13.980633  -39.880526  -39.880526
  103   23.435746  -18.989008  -18.989008
  166   40.677965  -47.603296  -40.139092
  140   41.618153  -58.673183  -17.608048
  138   20.019576  -40.846443  -14.799018
  136   31.455437  -50.511226   -6.454728
  217   27.721144  -61.249085  -61.249085
  223   57.908348  -32.912267  -32.912267
  207   17.242646   -1.511570  -55.993560
  267    6.517910   -9.434497   -9.434497
  259   18.807235  -98.790074  -81.566930
  9      2.951997  -89.245030  -39.208345
  274  132.999115  -88.597205  -88.597205
  122   28.638471  -91.373880  -50.638201
              ...         ...         ...

  [277 rows x 3 columns]